Wireless communication systems such as WCDMA (Wideband Code Division Multiple Access) LTE (Long Term Evolution), and LTE-A (LTE-Advanced) developed by 3GPP (Third Generation Partnership Project), and Wireless LAN and WiMAX (Worldwide Interoperability for Microwave Access) under IEEE (The Institute of Electrical and Electronics engineers) are configured as follows. A base station (cell, transmission station, transmission device, eNodeB) and a terminal (mobile terminal, reception station, mobile station, reception device, UE (User Equipment)) each have a plurality of transmission/reception antennas, and spatially multiplex data signals using MIMO (Multi Input Multi Output) technology to realize high-speed data communication.
The base station needs to control the terminal in various ways in the wireless communication system in order to realize data communication between the base station and the terminal. To this end, the base station informs the terminal of control information using a predetermined resource, thereby performing data communication in a downlink and an uplink. For example, the base station informs the terminal of resource assignment information, data signal modulation and encoding information, spatial multiplexing order information for data signals, transmission power control information, and so forth, thereby realizing data communication. Such control information can be informed using a method according to NPL 1.
Also, various methods can be employed as a communication method employing the MIMO technology in a downlink. Available examples of these methods include the multiuser MIMO format for assigning the same resource to different terminals, and the CoMP (Cooperative Multipoint) format where a plurality of base stations performing data communication by mutually collaborating.
FIG. 15 is a diagram illustrating an example employing the multiuser MIMO format. In FIG. 15, a base station 1501 performs data communication with a terminal 1502 through a downlink 1504, and performs data communication with a terminal 1503 through a downlink 1505. At this time, the terminal 1502 and terminal 1503 perform data communication by multiuser MIMO. The downlink 1504 and downlink 1505 use the same resource in the frequency direction and in the temporal direction. Also, beam control is performed using precoding technology or the like for the downlink 1504 and downlink 1505, thereby mutually maintaining orthogonality or reducing same channel interference. Thus, the base station 1501 can realize data communication with the terminal 1502 and terminal 1503 using the same resource.
FIG. 16 is a diagram illustrating an example employing the CoMP format. FIG. 16 illustrates a case where a wireless communication system having a heterogeneous network configuration is constructed using a macro base station 1601 having a wide coverage, and a RRH (Remote Radio Head) 1602 having a narrower coverage than the coverage of the macro base station thereof. Now, let us consider a case where the coverage of the macro base station 1601 includes partially or entirely the coverage of the RRH 1602. In the case of the example illustrated in FIG. 16, the heterogeneous network configuration is constructed using the macro base station 1601 and RRH 1602. The macro base station 1601 and RRH 1602 mutually collaborate to perform data communication with a terminal 1604 through a downlink 1605 and a downlink 1606, respectively. The macro base station 1601 is connected to the RRH 1602 through a line 1603, and can transmit/receive control signals and data signals to/from the RRH 1602. Available examples of the line 1603 include cable lines such as optical fibers, and wireless lines employing relay technology. At this time, each of the macro base station 1601 and RRH 1602 uses the same frequency (resource) partially or entirely, thereby improving overall frequency use efficiency (capacity of transmission) within the coverage area which the macro base station 1601 constructs.
In the case that the terminal 1604 is positioned nearby the macro base station 1601 or RRH 1602, the terminal 1604 can perform single cell communication with the macro base station 1601 or RRH 1602. Further, in the case that the terminal 1604 is positioned in the vicinity of an edge (cell edge) of the coverage which the RRH 1602 constructs, same channel interference from the macro base station 1601 needs to be dealt with. There has been studied a method for reducing or suppressing the interference as to the terminal 1604 at the cell edge area by employing the CoMP format wherein adjacent base stations mutually collaborate, by way of multi-cell communication (collaborative communication) between the macro base station 1601 and RRH 1602. A method according to NPL 2 has been studied as such a CoMP format, for example.